In a casting, metallic chills are used in order to provide progressive solidification or to avoid the shrinkage cavities. China CNC machining Chills are essentially, large heat sinks. Whenever , it is not possible to provide a riser for a part of the casting which is heavy, a chill is placed close to it as shown in Fig. 5.29, so that more heat is quickly absorbed by the chill from the larger mass making the cooling rate equal to that of the thin sections. Thus, this dose not permit the formation of a shrinkage cavity. But use of a chill means essentially providing higher cooling rate which is also likely to form a hard spot at the contract area with the chill and may therefore cause a problem if that area needs further processing way of machining.
The preparation of molten metal for casting is referred to simply as melting. Melting is usually done in a specifically designated area of the foundry, and the molten metal is transferred to the pouring area where the molds are filled. After moulding, melting is the major factor which controls the quality of the casting. There are a number of methods available for melting foundry alloys such as pit furnace, open hearth furnace, rotary furnace,China CNC machining cupola furnace, etc. The choice of the furnace depends on the cupola in its various forms is extensively used basically because of its lower initial cost and lower melting cost.
Cleaning refers to all operations necessary to the removal of sand, scale, and excess metal from the casting. The casting is separated from the mold and transported to the cleaning department. Burned-on sand and scale are removed to be improved the surface appearance of the casting. Excess metal, in the form of fins, wires, parting line fins, and gates,China CNC machining is removed. Castings may be upgraded by welding or other procedures. Inspection of the casting for defects and general quality is performed
Before shipment, further processing such as heat-treatment, surface treatment, additional inspection, or machining may be performed as required by the customer's specifications.